1. Field of the Invention
The present invention relates to a DC-DC converter and a voltage detector and particularly to a DC-DC converter for controlling a voltage induced at a secondary winding within a predetermined range and a voltage detector for measuring a voltage of a battery module using the DC-DC converter.
2. Description of the Related Art
In electric vehicles, hybrid vehicles, and fuel cell vehicles, motors are driven by a battery pack including a plurality of battery modules connected in series, each battery module including a plurality of cells. A voltage detector always monitors a voltage of each battery module, and a control unit performs a control to reduce dispersion in charging caused by deterioration in the battery modules.
A method of detecting voltages of battery modules is known in which one of photo-MOS switches selects one of battery modules to be measured, the voltage of the battery module is charged in a capacitor, and a voltage difference across both terminals of the capacitor is detected with an A/D converter.
JP 2006-153758 A discloses a technology in which the battery module voltage and a voltage having a value outside a voltage range where a battery modules possibly outputs are alternately applied to a capacitor by alternately switching the photo MOS switch and another semiconductor switch. A junction state, such as a status whether the battery module is disconnected from a measuring circuit, is determined on the basis of detection of variation in a voltage charged in the capacitor.
JP 2007-285714 A discloses a technology in which a variable resistor is connected to a photo-MOS switch, and a charging voltage is varied during switching of the photo-MOS switch. The junction status, such as a status whether the battery module is disconnected from the measuring circuit, is determined by determining whether an error occurs in time constant of charging voltage.